1. Field of the invention
The present invention generally relates to optical recording mediums and techniques for recording of information thereon. More particularly, the present invention relates to an information recording medium, preferably in the form of a disk or in tape format, suitable for use with an optical recording and playback apparatus.
2. State of the art
Optical recording methods have been proposed in which light from a laser is focused upon the surface of a recording medium with sufficient intensity to cause a detectable change in the physical characteristics of the surface material. Among these methods is the establishment of an information pattern of pits in the surface an optical medium. In such methods, the information representative pattern of pits can be formed in the surface of the recording medium by suitably controlling the intensity of the focused light in accordance with the information to be recorded while relative motion is established between the recording medium and the focused light spot.
Recently, there have been efforts to develop an information recording method in which information is written in a thin film of metal or the like formed on a substrate by using a laser ray or beam. According to such a method, information recording has been accomplished by forming holes or recesses in metallic thin films under the action of a thermal energy beam such as a laser ray. This method is suggested in , for instance, U.S. Pat. No. 4,238,803.
Dies and pigments have also been employed in information layers of recording media, often to enhance the sensitivity of the recording layers at the particular wavelength of the laser being used. Their use can provide a much sharper recording and playback of the information.
For example, U.S. Pat. No. 4,097,895 describes a recording medium which includes a light reflecting material, such as aluminum or gold, coated with a dye-containing light absorbing layer, such as a fluorescein layer which is operative with an argon laser light source. The thickness of the light absorbing layer is chosen so that the structure has a minimum reflectivity. An incident light beam then ablates, vaporizes or melts the dye-containing light absorbing layer, leaving a hole and exposing the light reflecting layer. After recording at the wavelength of the recording light, maximum contrast between the minimum reflectance of the light absorbing layer and the reflectance of the light reflecting layer exists.
Techniques for erasing the deformation pattern have involved reheating the thermoplastic film above its melting point to a significantly higher temperature than during recording in order to permit surface tension to smooth out the surface. Selective erasure may be accomplished by confining the heating to a selected area. After cooling, another deformation pattern may be recorded in the thermoplastic film.
For instance, U.S. Pat. No. 3,475,760, describes a system for directly recording information in a thermoplastic film as a deformation by using a high energy laser scanning beam of small diameter. The sensitivity of the films for laser film deformation recording can be enhanced by the addition of pigments or dyes which exhibit a high absorption at the laser wavelength. Erasure of the film deformation is accomplished by recording over the information to be erased using a similar laser beam but with a much smaller scan line spacing, preferably to provide overlap of the scan lines.
In a paper entitled "Single Wavelength Optical Recording in Pure, Solvent Coated Infrared Dye Layers" by Gravesteijn, Steenbergen and Van der Veen, experiments on the use of certain dyes for optical recording in digital and video applications at GaAlAs laser wavelengths are reported. The paper was presented at the Proceeding of the SPIE, "Optical Storage Media" Volume 420 Jun. 6-10 1983. The specific dyes discussed in the paper are squarylium dyes and pentamethine dyes. It is disclosed that solubility in organic solvents can be greatly increased by the introduction of t-butyl groups into thiopyrylium end groups. Other U.S. patents which disclose the use of a light absorbing dye in a recording layer include U.S. Pat. Nos. 4,412,231 and 4,446,223.
The use of dyes in conjunction with optical recording media comprising a styrene oligomer is disclosed in an article by Kuroiwa et al. appearing in the Japanese Journal of Applied Physics, Vol 22, No 2, February 1983, pp. 343-348. Among the dyes and pigments discussed as being useful is a copper phthalocyanine pigment. Phase separation and incompatibility between the dyes and oligomers are noted in the article as being problems in the use of dyes for optical information media.
U.S. Pat. No. 4,977,064 describes an optical recording medium of two recording media layers with each layer containing different light sensitive dyes. The two layers have individual specific reflectance, transmittance and absorbance which allows for detection of a variation in the amount of light reflected from the boundary between the two layers.
Various optical recording media have also been investigated. U.S. Pat. No. 4,478,782 describes an optical recording medium of a dimer acid polyamide in which information is recordable and erasable. U.S. Pat. No. 3,574,760 describes thermoplastic films utilized as erasable recording media. Suitable thermoplastic films are disclosed as including vinyltoluenebutadiene, polystyrene orthoterphenyl, polyethylene, and nitrocellulose.
The recording medium, of course, is one of the key elements in any optical recording system in which the information is recorded or read by light. Such a system would have usefulness in the storage of audio and video information, data processing and document processing. The commercial viability of an optical recording medium would depend upon such technical parameters as the sharpness in recording, playback of the information, and the useful life of the information medium. Maintaining the sensitivity of a recording medium throughout the cycles of record-read-erase is also an important consideration.
Although many different media have been investigated for possible use in the various aforementioned recording systems, and in particular the laser systems, a suitable recording medium or disk which is stable and economical, yet readily erasable when desired, has yet to be provided. Such a recording medium, would be readily accepted and would fill the void in the video recording market place. The search for improved, erasable optical recording media is ongoing.